Without you knowing it, toxicity can rub off on you.
When you give a toxic person more time and space in your life than they deserve, you might start being toxic as well – as an adaptive reaction to the bad relationship. These kinds of relationships bring out the worst in you, and the time will come when you will be disgusted at the person you have become.
For this reason, you should leave these relationships as soon as you can. Don't hesitate or second-guess yourself – just run and don't look back. Trust me that is the only way you can maintain your sanity and keep growing in a positive way.
Dating a serial cheater, a person you cannot trust at all, will slowly make you full of paranoia. You will become an undercover detective, looking through their phone, trying to get into their emails, grilling them about the girls they talk to and looking to see who they are interacting with on social media. And it's all because you believe that this person is out to hurt you another time. And yes, they will. But the solution is not to watch their every move. Your best option is to pack up and leave. Staying will lead you to become a shell of your former self, and you will have no idea who you are anymore.
Once you involve yourself with someone who makes an argument out of everything, a person who is filled with rage at the slightest provocation, and someone you can no longer have a cordial chat with without voices getting raised, you start looking deep within you. You watch what you say and do. You can no longer share anything exciting about your day as that might set off their jealousy. You shop in secret, even with your own money, because that might make them mad. You always delete your browser history, however innocent, because it might make them upset. You turn into a liar and someone who sneaks around and the truth becomes a fearful thing for you and you avoid it. Yes, you should have left them, but you held on, and now you have no idea whom you have become anymore.
You involved yourself with a person who thinks drama over jealousy is the idea of romance. They get into fights with you just to have fun, and you are starting to think arguments are normal. In the heat of the situation, you say things you regret. Shouting matches become a regular thing for you. You start to like the drama and look forward to it, as you have slowly become an addict. The misery appears like comfort to you, and you think fighting is a sign of passion. You did not leave, and staying has made you someone you don't know.
As much as you want to fight for your partner, a toxic relationship will be self-destructive in the end. It's perfectly fine if you leave and start anew.
Staying in a bad relationship will slowly destroy who you are and make you someone you don't even recognize.
The answer is getting out now so that you can work on your trust, abandonment, and commitment issues. You can be a healthy and normal person again, but it will take some effort.
But get this right - the decision to leave, forgive yourself, and work on being a better version of yourself is all yours and nobody else's.